pidl: Fix array range checks in python output

pidl: Fix array range checks in python output

Without this, we generated code like

if (ndr_table_dnsserver.num_calls < 0) {
        PyErr_SetString(PyExc_TypeError, "Internal Error, ndr_interface_call missing for py_DnssrvOperation_ndr_pack");
        return NULL;
}
call = &ndr_table_dnsserver.calls[0];

This does not really make sense, and Coverity found comparing the unsigned
num_calls against <0 a bit pointless.

Should fix 138 Coverity findings and make the code a bit more correct.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>